1. Field of the Invention
This invention concerns a polyvinyl alcohol polymer production method and a polyvinyl alcohol polymer (hereinafter, polyvinyl alcohol shall be abbreviated as xe2x80x9cPVAxe2x80x9d). To be more specific, this invention concerns, along with PVA, a method of producing PVA polymer by saponifying a polyvinyl ester in an alcohol-containing organic solvent under the presence of a saponification catalyst and with which the saponification reaction is carried out while distilling off the carboxylic acid ester that is produced by the saponification reaction.
2. Description of the Prior Art
For producing PVA, the method in which vinyl acetate is obtained by acetoxylation of ethylene, polymerizing this vinyl acetate to obtain polyvinyl acetate, and saponifying this polyvinyl acetate under the presence of a basic catalyst is used generally and practiced industrially as well. As methods of saponification, methods that use various types of saponifiers, such as the belt type, pipe type, slurry type, etc., are known, and the PVA that is obtained by saponification by such methods is made into powder, dried, and then used in various applications. In industrial material applications and composite material reinforcement applications, an aqueous solution of PVA, obtained by dissolving powder-form PVA in water, is used as the spinning stock solution, and spinning is performed by a wet, dry-wet, or other type of spinning method to use the PVA in the form of PVA fiber. However, when the content of sodium acetate in the PVA is high, the fiber obtained by making the PVA into fiber may at times be colored. Moreover, acid is required for adjusting the degree of saponification of PVA, and the equipment tends to be large in scale.
In recent years, methods of spinning PVA in an organic solvent to produce high-strength PVA fibers more suitable for industrial material and composite material reinforcement applications are being examined. For example, Japanese Laid-open Patent Publication No. 40807/1991 discloses a method of producing PVA fiber by spinning a PVA solution obtained by saponifying a polyvinyl ester having a high degree of polymerization in an organic solvent. With this method, the organic solvent used for the polyvinyl ester saponification process may be used in common as the organic solvent used in the spinning process in which the PVA polymer solution is spun, and a rational PVA fiber production process in which the saponification process and the spinning process are linked directly can be constructed.
However, in order to raise the degree of saponification of PVA in cases where alcohol is used to saponify the polyvinyl ester, the mole ratio of methanol with respect to PVA must be made high. However, if the mole ratio of methanol with respect to PVA for increasing the degree of saponification of PVA is made too high, the PVA gels, and since a large amount of organic solvent, such as dimethyl sulfoxide (DMSO), must thus be used to prevent gelling, the concentration of the PVA that was obtained was only a few % at the most. With the present invention, in the case where only polyvinyl ester exists, the mole ratio of alcohol with respect to PVA shall refer to the mole ratio with respect to the amount of PVA as determined based on conversion of all of the polyvinyl ester to PVA, and in the case where PVA and polyvinyl ester coexist, the mole ratio of alcohol with respect to PVA shall refer to the mole ratio with respect to the amount of the PVA that already exists and the amount of PVA as determined based on conversion of all of the polyvinyl ester to PVA. This mole ratio shall hereinafter be referred to simply as the mole ratio of alcohol. Also with this invention, the concentration of PVA polymer in the saponification reaction solution shall refer to the concentration of the PVA generated by the saponification reaction plus the PVA as determined based on conversion of the unreacted polyvinyl ester to PVA in the organic solvent from which alcohol has been excluded.
If a high-strength PVA polymer with a higher degree of saponification than those of prior arts can be obtained, this will be beneficial industrially and if the organic solvent used in the polyvinyl ester saponification process can be used in common as the organic solvent used in the spinning process in which the PVA polymer solution is spun and the PVA concentration can be increased further, the saponification process for the PVA polymer and the spinning process for making the PVA polymer into fiber can be linked directly to make the PVA fiber production process a rational process with higher productivity. Also, if a PVA polymer production method can be established with which the mole ratio of alcohol can be selected freely and the degree of saponification of PVA polymer and the concentration of PVA polymer can be adjusted freely, it will become possible to produce PVA polymers suited for various needs.
Thus a first object of this invention is to provide a method of producing PVA polymer, with which a PVA polymer, which has a higher degree of saponification than those of the prior arts and can be used as raw material for high-strength fibers, may be obtained at a low mole ratio of alcohol.
A second object of this invention is to provide a rational method of producing PVA polymer, which does not require the processes of drying, pulverizing, and dissolving the PVA in organic solvent, with which the saponification process for the PVA polymer can be directly linked to the spinning process for making the PVA into fiber, and with which the concentration of PVA polymer will be high and the content of sodium carboxylate in the PVA polymer will be low.
A third object of this invention is to provide a method of producing PVA polymer, with which the mole ratio of alcohol with respect to polyvinyl carboxylate can be freely selected and the degree of saponification of PVA polymer and the concentration of PVA polymer can be freely adjusted.
A fourth object of this invention is to provide a method of producing PVA polymer fiber in which the polyvinyl ester saponification process is directly linked with the spinning process in which the PVA polymer solution, obtained by the saponification process, is spun.
A fifth object of this invention is to provide a PVA polymer, which has a block character value of 0.9 to 1.1 and is high in randomness.
However, as has been mentioned above, the operation for increasing the degree of saponification of PVA conflicts with the operation for raising the concentration of PVA. In order to establish a method of producing PVA polymer that meets the above objects, the present inventors have repeatedly examined the polyvinyl ester saponification reaction in detail and have come to make the present invention. That is, the present invention provides in a method of producing polyvinyl alcohol polymer, in which a polyvinyl ester is saponified in an alcohol-containing solvent under the presence of a saponification catalyst, a method of producing polyvinyl alcohol polymer characterized in that the saponification reaction is carried out while distilling off the carboxylic acid ester that is produced by the saponification reaction.
This invention also provides a method of producing PVA polymer fiber in which the polyvinyl ester saponification process is directly linked with the spinning process in which the PVA polymer solution, obtained by the saponification process, is spun.
This invention furthermore provides a PVA polymer, which has a block character value of 0.9 to 1.1 and is high in randomness.
By this invention, a high-strength PVA polymer, which is excellent in randomness and has a higher degree of saponification than PVA polymers of the prior art, can be obtained. Also with this invention, since the rate of saponification of polyvinyl ester is fast and a PVA polymer can be obtained at high concentration in an organic solvent, the polyvinyl ester saponification process can be directly linked with the spinning process, in which the PVA polymer solution is made into fiber, and since the mole ratio of alcohol can be selected freely and the degree of saponification of the PVA polymer that is obtained can be adjusted freely, a rational PVA fiber production process can be constructed.